Field of the Invention
The present invention relates to an image shake correction device, an optical apparatus, an imaging apparatus, and a control method.
Description of the Related Art
An optical shake correction method and an electronic shake correction method have been proposed as methods that correct the shaking of a captured image (image shake) caused by shaking applied from the outside to an imaging apparatus, for example, a camera or a video. In the optical shake correction method, a lens and an imaging element are driven and the image shake is optically corrected. In the electronic shake correction method, a extraction position and the like of an image obtained by photoelectrically converting light that has been input to an imaging element is changed and the image shake is corrected.
In recent years, with the spread of the imaging apparatuses including a camera or a video and with the change of its manner of use, the demand for an imaging apparatus that enables simultaneously shooting moving images and still images by single apparatus is increasing. However, while the moving image has an image representation in which a change with the passage of time of the image is displayed, the still image has an image representation in which an image at a specific moment is extracted. Due to such differences in the image representation, there are many differences between the shooting of moving images and the shooting of still images in the control while shooting by a camera, for example, hand shake correction (image stabilizer: IS), auto focus (AF), and exposure control (automatic exposure: AE) while shooting by a camera. For example, with regard to shake correction control, in the shooting of moving images, the continuity between frames, in other words, smoothness of the motion with the passage of time, is more important even if motion blur of the moving image is present in the image. In contrast, the shooting of still images provides an image that captures a specific moment and needs sharpness without blur in the main subject.
Thus, while shooting moving images, a high-pass filter (HPF) is applied to a shake signal that has been detected and a low frequency component is removed, and as a result, a situation in which a shake correction unit reaches a limiter on control and correction is made impossible is avoided as much as possible even if slow shaking remains. In contrast, during the exposure in still image shooting, the high-pass filter (HPF) is not applied to the shake signal that has been detected and the correction of all shake components including the low frequency component is allowed, and the improvement of the performance has been attempted.
In this context, as a method of detecting shake signals, although there is a method that detects vibrations of a camera by using a sensor that detects acceleration, angular acceleration, an angular velocity, and angular displacement, and the like, a gyro sensor that detects the angular velocity is commonly used as a sensor for detecting the vibrations of camera. However, the gyro sensor is largely affected by DC offset and drift due to a temperature change, and thus a mechanism for removing the offset component from a reference value is necessary. Although this offset component can be removed if the HPF is applied to the vibration signal from the gyro sensor, it cannot be removed if the HPF is not applied, causing a deterioration in the anti-vibration performance due to the deviation of the reference value.
Japanese Patent Application Laid-Open Publication No. 2009-244853 discloses an imaging apparatus in which an intermediate value held as a calculation result for each of control samples of a digital high-pass filter (HPF) and a digital offset to be added to a shake output are changed, and the offset component included in the shake output is removed. Additionally, Japanese Patent Application Laid-Open Publication No. 2008-283443 discloses an imaging apparatus in which switch setting whether or not HPF processing is performed in accordance with the exposure time, and thus the influence on an accuracy of the image shake correction by HPF processing is reduced.
The imaging apparatus disclosed in the Japanese Patent Application Laid-Open Publication No. 2008-283443 has a the following inconvenience because a motion while switching the HPF is not taken into account. Specifically, when the HPF is not applied while shooting moving images (for example, when the EVF is used) , the low-frequency component is also corrected, causing a difficulty in the framing, and in addition to that, causing a correction unit such as a shift lens to easily hit the limiter (correction end). Additionally, if a path of the shake signal processing is divided into two, specifically, the presence/absence of the HPF, between the exposure of still images and the shooting of moving images, the signal causes a discontinuity while switching the HPF, and thereby the correction unit moves significantly.